The present invention relates to network management in general, and more particularly to an interface of a network manager to a network of communication devices in which an input and an output port of the devices are coupled together in a daisy chain to form a single communications channel.
Generally, wide area type dial modem networks use a network manager to monitor the status of a pool or network of modems to determine malfunctioning modem(s) and to take steps to circumvent selection of the malfunctioning modem(s), for example, so that proper operation of the network may continue. The network manager may be local to the modem pool or be coupled through a lease line connection from a remote location via a public system telephone network (PSTN).
A problem arises in interfacing the network manager with each pool of modems which may be in the hundreds. It would be cost prohibitive to couple each modem of the pool to the network manager through a separate channel, like a EIA 232 interface, for example. In small pools of modems, a special Y cable is used to couple up to four modems to the network manager using a modified EIA 232 interface. For larger modem pools, an external digital sharing device (DSD) is used to couple N modems to the network manager using a separate DSD port for each modem. The first method, of course, is limited to a physical connection of only four modems to an input port of the network manager which is capable of handling a much larger number of modems from a load point of view. Further, while the second method using the special external DSD permits many modems to interface with a single port of the network manager, each port connection of the DSD is very costly. The same problems are encountered in the cases of remotely located modem pools, but are additionally compounded somewhat because crossover cabling is needed for coupling a remote master which receives signals from the network manager through the PSTN, for example, to the remote pool of modems using either the foregoing described first or second method.
It is desired to simplify the interface cabling needs between the network manager and its pool of modems by eliminating Y cabling and crossover cabling and further, reduce costs by eliminating any need for an external DSD unit. The present invention provides an interface between the network manager and a pool of modems which achieves these objectives.